Deep Impact
First Look Inside a Comet
Michael F. A’Hearn
Outline
1.
2.
3.
4.
5.
6.
Why Study Comets?
Scientific Objectives, Mission Overview, Context
Cratering Physics
The Target and Its Environment
Instruments and Measurements
How you can participate
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 2
Why Study Comets?
The Independent 1996
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 3
More Reasons Why
C/Bennett 1970 II
C/Lee 1999 H1 - L. Sanino
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 4
Cometary Dichotomies
•
•
•
•
•
•
Comets have the most primitive,
accessible material in the SS
Comets must become dormant
There must be many dormant
comets masquerading as NEAs
We know more chemical and
physical details than for other
small bodies in the SS
Abundances in the coma are
used to infer ices in the protoplanetary disk
Comets break apart under small
stresses
ESO - 14 Feb 2004
•
•
•
•
•
•
We do not know what is hidden
below the evolved surface layers
Is the ice exhausted or sealed in?
We can not recognize dormant
comets among NEAs
We do not know how to use these
details to constrain models of
nuclei
Abundances in the coma differ
significantly but in unknown
ways from nuclear abundances
Variation of strength with scale is
totally unknown
Deep Impact - First Look Inside a Comet
mfa - 5
Dormant Comets
•
•
Earlier “best” cases (Oljato, Phaethon, etc.) showed anomalous,
possibly cometary properties but were not good analogs in other
ways
Recent examples very likely to be comets
– Tisserand invariants <3, including retrograde objects
– Low albedos (all <0.1, most <0.06)
– Data from several sources beginning with Harris et al. 1999, Y.
Fernández et al. 2003
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 6
Dormant Comets
Convincing evidence for dormant comets!!
(at last)
- cometary nuclei
NEAs & UAs, T<3
NEAs & UAs, T>3
Y. Fernández et al. 2002
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 7
Nuclear Models
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 8
Interior Model?
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 9
Evolutionary Models
Benkhoff-Huebner model has density increasing
monotonically from surface to 10s of meters. PrialnikMekler model has a dense layer of water ice at surface
with lower density material below.
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 10
Differences Among Nuclei
QuickTime™ and a YUV420 codec decompressor are needed to see this picture.
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Stardust Team
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
L. Soderblom
mfa - 11
2. Scientific Objectives, Mission Overview, Context
Also Hidden - Inside the Nucleus
Deep Impact -
- An artificial meteorite impact
- 370 kg at 10.2 km/s
- Are there pristine ices at depth?
- What are the surface material properties?
Unlike SL-9 at Jupiter, we will know everything
about the impactor so the only unknowns are in
the target
"It [an asteroid] was racing past them at almost thirty miles a second;
they had only a few frantic minutes in which to observe it closely. The automatic cameras took dozens of photographs,
the navigation radar's returning echoes were carefully recorded for future analysis - and there was just time for a single
impact probe.
The probe carried no instruments; none could survive a collision at such cosmic speeds. It was merely a small slug
of metal, shot out from Discovery on a course which should intersect that of the asteroid.
.....They were aiming at a hundred-foot-diameter target, from a distance of thousands of miles...
Against the darkened portion of the asteroid there was a sudden,
dazzling explosion of light. ...”
____________________
Arthur C. Clarke, 1968. In 2001: A Space Odyssey. Chapter 18
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 13
Science Team
M. F. A’Hearn, PI
Management, Emission Spectra,
Coma relation to nucleus, PDS
Archiving
M. J. S. Belton, Deputy PI
Imaging, Rotation
A. Delamere
Instrumentation
J. Kissel
Dust, Ejecta from crater
K. Klaasen
Mission operations, Geomorphology
L. A. McFadden, EPO Dir.
Outreach, Reflection Spectroscopy,
geology
K. J. Meech
Earth-based observing program
H. J. Melosh
Cratering - numerical simulations
P. Schultz
Cratering - experiments
J. Sunshine
Reflection spectroscopy, analysis
J. Veverka
Relation among comets & asteroids,
Data processing pipeline
D. K. Yeomans
Dynamics, Radio science
P. Thomas
Shape Model, Geomorphology
Associated Scientists
T. Farnham, Y. Fernández, C. Lisse, D. Wellnitz
Occasional support from numerous others, including
T. Ahrens, J.D. O’Keefe,J. Pittichova, D. Scheeres
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 14
Context – Other Small-Body
Missions
Mission
Launch
Encounter
Encounter
Encounter
Land
End Mission
NEAR
1996
Feb 17
1997 Jun 27
Mathilde
1998 Dec 23
Eros
2000 Feb 14
Eros
2001 Feb 12
Eros
2001 Mar
DS-1
1998
Oct 25
1999 Jul 28
Braille
2001 Sep 23
Borrelly
Stardust
1999
Feb 12
2002 Nov 2
Annefrank
2004 Jan 2
Wild 2
Contour
2002
Jul 3
2003 Nov 11
Encke
2006 Jun 18
S-W 3
Muses C
2002 Dec
2005 Sep
(25143)
2001 Oct
2006 Jan 15
Earth
2008 Aug 18
D’Arrest
2011 Jul 27
Wirtanen
2014 May 23
ChurymovGerasimenko
2006 Jan
2006 Jul
2003 Aug
2007 Jun
Earth
2007 Jun
2012 Mar
Wirtanen
2014
Chur-Ger
2014
2015 Aug
Rosetta
2003 Jan 12
2004 Feb 26
2006 Jul 10 Otawara
TBD
2008 Jul 23
Siwa
Deep Impact
2004
Dec 30
2005 Jul 4
Tempel 1
2008 Nov
Boethin
2005 Aug
Dawn
2006
May 27
2010 Jul 30
Vesta
2014 Aug 20
Ceres
2015
KBP
2006 Jan
2007 Jan
Jupiter
2015
Pluto
ESO - 14 Feb 2004
?
KBO
Deep Impact - First Look Inside a Comet
?
KBO
?
mfa - 15
Scientific Objectives
•
Primary Scientific Theme
– Understand the differences between interior and surface
– Determine basic cometary properties
– Search for pristine material below surface
•
Secondary Scientific Theme
– Distinguish extinction from dormancy
•
Additional Science Addressed
– Address terrestrial hazard from cometary impacts
– Search for heterogeneity at scale of cometesimals
– Calibration of cratering record
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 16
Mission Overview
•
•
2 spacecraft – Smart Impactor + Flyby
Fly together until 1 day before impact
– 6-month Earth-to-comet trajectory
•
Smart Impactor
– Impactor Targeting Sensor (ITS)
• Scale 10 microrad/pixel
• Used for active navigation to target site
• Images relayed via flyby to Earth for analysis
– Cratering mass (~360 kg at 10.2 km/s)
• Excavates ~100-meter crater in few*100 seconds
– Baseline prediction - other outcomes are possible
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 17
Mission Overview (continued)
•
Flyby Spacecraft
– Diverts to miss by 500 km
– Slows down to observe for 800 seconds
– Instruments body-mounted – spacecraft rotates to follow comet
during flyby
•
Instruments on Flyby Spacecraft
– High Resolution Imager (HRI)
• CCD imaging at 2 microrad/pixel (0.4 arcsec/pixel)
• 1-5 micron long-slit spectroscopy (R>200, 10 microrad/pix)
– Medium Resolution Imager (MRI)
• CCD imaging at 10 microrad/pixel
• Identical to ITS but with filter wheel added
•
Major Earth-based Observing Campaign
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 18
Spacecraft Overview
Instruments
MRI, ITS, HRI
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 19
Interior View Of Flyby Spacecraft
Propulsion Tank Will Replace Ron
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 20
Inter-Planetary Trajectory
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 21
Encounter Schematic
Impactor Release
E-24 hours
AutoNav Enabled
E-2 hr
ITM-1 Start
E-88 min
ITM-2
E-48 min
ITM-3
E-15 min
Tempel-1
Nucleus
64
kbps
2-way
S-band
Crosslink
500 km
Flyby S/C
Deflection Maneuver
E-23.5 hr
Science and
Autonav Imaging to
Impact + 800 sec
Flyby S/C Science
And Impactor Data
at 175 kbps*
Flyby Science
Realtime Data
at 175 kbps*
Shield Mode
Attitude through
Inner Coma
TCA +
TBD sec
Flyby S/C Science
Data Playback at 175 kbps*
to 70-meter DSS
* data rates without Reed-Solomon encoding
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
Look-back
Imaging
mfa - 22
3. Cratering Physics
Which physics will matter?
Possible Scenarios
•
Crater formation on an intact nucleus
– Gravity controlled crater
– Compression controlled crater
•
•
Split nucleus
Crater formation on an intact nucleus
– Strength controlled crater
•
•
•
Aerogel-like capture of the impactor
Shattered nucleus
Transit through the nucleus
•
Above are roughly in order of decreasing probability (as
guessed by the PI)
N.B.: K.E. of Impactor << Gravitational Binding Energy of
Cometary Nucleus
N.B.: v2/2 > maximum energy per mass of any chemical
explosive
•
•
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
D. K. Yeomans
CSR page 1-12
mfa - 24
Cratering Physics
• Gravity control expected
–
–
–
–
Size and time sensitive to cometary properties
Size ~ (impactor mass)1/3
Size insensitive to other properties
Details of early ejecta (speed, jets) sensitive to shape and density
Strength control possible
Size depends on impactor density (as does speed of early ejecta) –
much smaller than under gravity control;
greater depth/diameter than under gravity control;
details sensitive to shape of impactor
Compression control possible
Scaling relationships not known
Mechanism proposed to explain Mathilde’s craters
Schultz’s experiments with perlite suggest it occurs when “particles” are
comparable in size to impactor
Distinguish mode by ejecta morphology and crater size
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 25
Ejecta Cone
Figures are for gravity
controlled situations.
If strength controlled,
cone detaches from
surface.
If volatiles exist under
inert material,
vaporization drives
ejecta that tend to fill
in cone.
If compression
controlled, much less
total ejecta in cone
and no final rim.
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 26
Cratering Experiments
Gravity Control
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
QuickTime™ and a
Video decompressor
are needed to see this picture.
At Ames Vertical Gun, P. Schultz
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 27
Formation Time Scaling
Different Cometary Bulk Densities
m1/6
T~
T ~ rc-2/3
T ~ Rc-2/3
550
50
450
Crater Formation Time (s)
800-sec observing
window provides large
margin for extreme
cometary properties,
even down to bulk
density 0.1 g/cc
(Affects Gravitational Acceleration)
400
350
300
250
200
Surface Density = 0.3 g/cc
150
100
200
400
600
1000
Im pactor Mass (kg)
Most important thing is to know impactor properties
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 28
Impactor Designed to Optimize
Cratering
Debris
Shields
note:
radiator not
shown is
debris shield
too
Launch vehicle adaptor not shown
Design simplifies adding mass at start of I&T
Stacked plates can easily be made porous
Science traded less copper for more front mass
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
Radiator shown in
translucent blue
mfa - 29
Crater Mass Design
Impactor Spacecraft Specification Compliance Verification
Cratering Mass Requirements
Method
3.2.4.6.1-1a Concentrate as much
Meet
Analysis
mass as possible in the forebody.
Analysis
3.2.4.6.1-1b Provide for flexibility in
Meet
Inspection
Impactor dry mass.
3.2.4.6.1-1c Forebody to approximate
Meet
Analysis
a hemispherical profile.
3.2.4.6.1-1d Average (nonhomogeneouse) forebody density in the
Meet
Analysis
range of 2.5-5.5 gm/cc, with higher
3.2.4.6.1-1e Forebody diameter > .5
meter and a diameter to depth ratio
Meet
Analysis
between 2:1 and 4:1.
Comments
Minimize structure mass using
material choices and analysis
Mass can be adjusted within 80144 kg.
Hemispherical shape with
cutout for ITS
Density range 3.0-5.5 gm/cc
Diameter .64 meter
Diameter to depth ratio 4:1
Largest disk
15.8 Kg (38 lbs) min weight
Mass 7 disks bolted together
Match drilled pins for shear
Located in the forebody
Mounted to the main deck
Disks C11000 copper
Each disk chamfered to
approximate a sphere
Cutout for ITS
Specific values documented in SER
DI-IMP-STR-006
37.2 Kg (82 lbs) max weight
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 30
Impactor Mounting Ring Installation
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 31
Speed of Early Ejecta
Solid Copper
Porous Copper
Ejecta Velocities
Comparison
PLATE porous
~ 0.5-1.5 km/s
CAP solid
~ up to 5 km/s ,
high initial
temperatures
Porosity of
plate reduces
ejecta velocity!
Easier to track
ejecta!
J. D. O’Keefe
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 32
Baseline Prediction
•
•
Assumes Gravitationally Controlled Crater
Final Crater
– Diameter ~110m
– Depth ~ 27m
– Formation Time ~ 200 s
•
Phenomena
–
–
–
–
–
–
•
Bright, optical flash, <1 sec
Hot (>1000K) ejecta for 10s of seconds, gradually cooling
Max velocity ~ 2 km/s, decreasing to < escape velocity (~2 m/s)
Mass of ejecta from crater (4 min) ~ natural ejecta in 1 week
Negligible quantity of “boulders”
Clumping of ejecta to allow tracking?
Long-term changes
– New “active area”
– Outgassing jet that may last days to months
– Increased ratio of CO & CO2 to H2O
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 33
4. Target Properties - 9P/Tempel 1
What Can We Know Before Impact?
Wilhelm Tempel
Target Update – Nucleus
•
Size and albedo
– Keck #1 + UH 88”, 2000 August 21; poor weather
– <R> = 2.6±0.5 km, pR ~ 0.07±.03
– Fernández et al. 2003
•
Rotation
– UH 88” – many runs, HST – 1 run, several runs at Lowell and ESO and La
Palma, selected data from various other sites, - all except HST since Jan
1999
– Partially analyzed – P ~ 41 hours or ~21 hours
– Axis orientation and sense of rotation MAY be determinable well before
impact, but not yet confident
•
Shape
– Axial ratio > 1.3, probably > 2, possibly ~3
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 35
Nuclear Radius
Keck, thermal IR (10.7 mm), 21 Aug 2000 composite
Radial profiles of thermal IR image
separate dust from nucleus
UH 88”, optical (0.7 mm), 21 Aug 2000
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 36
Slow Rotation of 9P/Tempel 1
P/Tempel 1 Mar 1999 data (Meech et al)
Model: P=1.7478; a=5.8,b=c=3.28km; A=0.04; C-type Hapke; Phi=180@JD2451206.94898
16.0
15.9
15.8
15.7
M(1,1,a)
15.6
15.5
15.4
15.3
15.2
15.1
15.0
2451253
2451254
2451255
2451256
2451257
2451258
2451259
2451260
2451261
2451262
2451263
Julian Days
P/Tempel 1 All 1999 data (Meech et al)
Model: P=1.7478 d; a=5.8,b=c=3.28km; A=0.04; C-type Hapke; Phi=180@JD2451206.94898
16.0
15.9
15.8
15.7
15.6
15.5
M(1,1,a)
15.4
15.3
15.2
15.1
15.0
14.9
14.8
14.7
14.6
14.5
2451197
2451207
2451217
2451227
2451237
2451247
2451257
Julian Days
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 37
IRAS Survey Image
Tempel 1
Dust Trail in Orbit Plane
Best image of dust
trail from comet
Tempel 1. 1983
Zodiacal
Dust
Density of old dust in
orbit plane is low
compared to dust
currently released near
nucleus!
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 38
Revised IRAS Results Limit Dust
R. Walker
HCON 421
R=1.56
D=1.26
Trail visible
but very faint
ESO - 14 Feb 2004
Improved spatial resolution and better flux
calibration (10-50% fainter; 25K hotter).
These are the only data sensitive to large
(> 10 mm) particles in inner coma.
HCON 339 1983 Jul 13, T+5 days
HCON 421 1983 Aug 24, T+46 days
Deep Impact - First Look Inside a Comet
mfa - 39
Design Dust Model
Steeper power laws inconsistent with IRAS data - lack of 10-mm silicate emission
Shallow power laws, such as m-0.2, inconsistent with optical data
No data very sensitive to particles with m > 0.1 g
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 40
5. Instruments and Measurements
Instrument Platform Assembly for Flyby
Spacecraft Maintains Instrument and ACS
Sensors in Alignment
Star
Trackers
Debris
Shielding
HRI
Instrument
IRU
Low Gain
Antenna
Instrument
Platform
ESO - 14 Feb 2004
MRI
Instrument
Deep Impact - First Look Inside a Comet
mfa - 42
Instrument Platform
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 43
Visible Imagers
Parameter
HRI
MRI
ITS
FOV [mrad]
2.05
10.2
10.2
IFOV [mrad]
2
10
10
Dl [mm]
0.3-1.0
0.3-1.0
0.3-1.0
PSF FWHM
[pix@0.7mm]
<2.2
<0.9
<0.9
Full Frame
Rate [s-1]
1/1.7
1/1.7
1/1.7
Radiometric
Sensitivity
Stars to
m~11.3 in 0.1
s
Stars to
m~11.3 in 0.1
s
Stars to
m~11.3 in 0.1
s
Boresight
Alignment
<1 mrad
<1 mrad
N/A
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
CCDs
1024x1024 active
area
Bilateral frame
transfer
(2 1024x512
shielded areas)
mfa - 44
IR Spectrometer
Parameter
Capability
Units
Slit FOV
2.6
Mrad
IFOV
10
mrad
Dl
1.05-4.8
mm
PSF FWHM
<1
Pix@2.5mm
Resolving
Power, l/dl
744@1.04mm
209@2.6mm
385@4.8mm
Radiometric
Sensitivity
<200
kR/dl at CO
(4.7 mm)
Full Frame
Rate
1/1.75
s-1 for 1.75s
exposure
ESO - 14 Feb 2004
Detector
Rockwell HgCdTe with
“Hawaii” MUX
1024x512 with 2x2
readout binning
Deep Impact - First Look Inside a Comet
mfa - 45
CO Lines Drive HRI IR Sensitivity
1400
H2O
Surface Brightness (kR)
1300
150 K
145 K
140 K
135 K
CO Requirement
Pre-Impact
3.5 um Requirement
1200
1100
1000
900
800
700
600
500
H2CO
CO 2
400
300
200
100
CO
0
2.5
3.0
3.5
4.0
4.5
5.0
Wavelength (microns)
Currently expected operating temperature of optical
bench is 135K
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 46
High Resolution Instrument (HRI)
Overview
HRI Telescope
HRI Spectral
Imaging
Module (SIM)
View Looking down HRI Boresight
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 47
:16:13
HRI Spectral Imager Module (SIM)
Layout
JBAER
•2-prism design (CaF2 & ZnSe)
•Large etendue, no order separation
•f/12 camera (3x reduction)
TM2 S26
11:02:56
DGALLAGH
PR2 S21-24
PR1 S17-20 CLM1 S15
FM3 S27
TM3 S29
BS S8-9
75.00
HRI rebuild TM1
7
S13
Positions:
SLIT S12
1-3 JWB
MM
4-Feb-01
75.00
HRI-SIM
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
HRI-SIM
DJG
MM
30-Oct-01
mfa - 48
SIM Assembly
With the spectral imaging
module on the optical bench,
theodolites are used to align
the mirrors and prisms.
Eighteen days were needed
for aligning and locking the
optics in place.
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 49
Impactor Measurements
•
•
Images for navigation as needed
Images for science at intervals of √d, where d is distance from
impact
– Early images are full frame
– Later images are sub-frames, down to 128x128, due to limitations of Sband link from impactor to flyby
– Best resolution if no dust hits - 20 cm
– Best resolution if dust hits are major problem - 1.5 m
•
Largest challenge
– Knowing time of impact in order to know when to switch image sizes
– A priori time ±30s 3-s
– Determine to ±5s 3-s from flyby rotation and uplink to impactor in
order to shift image sequence in time
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 50
Flyby Measurements
•
Before impact
–
–
–
•
At time of impact
–
–
•
Images of ejecta cone
Spectra of down-range ejecta
Track ejecta with images
After crater complete
–
–
–
•
High speed imaging subframes (1282)for light curve, initially dt < 0.17s
Shift to full frame at slower rate as time increases
Shortly after impact until crater completely formed
–
–
–
•
Monitor rotation of nucleus (brightness) & coma activity for weeks
Map coma with narrow-band filters
Map nucleus & innermost coma in filters and with spectrometer
Map nucleus & crater in filters and spectrometer
Spectra off limb for changes in outgassing
Final crater image with resolution ~ 3-4m
Look-back imaging
–
–
ESO - 14 Feb 2004
Minutes to hours after flyby
Images and spectra to study changes in activity and map other side of nucleus
Deep Impact - First Look Inside a Comet
mfa - 51
Sample Data
•
ESO - 14 Feb 2004
Barringer Meteor Crater seen with
comparable number of pixels as
Deep Impact crater assuming
nominal model for cratering
Deep Impact - First Look Inside a Comet
mfa - 52
Analysis Approach
•
•
•
•
•
•
•
•
Determine cratering regime debris cone detachment, lack of
ejecta
Confirm regime from scaling
relations
IF GRAVITY DOMINATED (i.e., one
possible analysis scenario)
Estimate porosity from half-angle
of debris cone
Estimate subsurface structure
from blockiness of crater walls
Estimate density ratio of impactor
to target from shape of
expanding plume
Determine buried ices from gasdriven jet pushing through ejecta
Determine layering of regolith
from crater walls
ESO - 14 Feb 2004
•
•
•
•
•
Determine coefficients for scaling
laws applicable to small bodies in
the solar system
Determine composition of ejected
debris from downrange near-IR
spectra
Estimate differentiation of ices by
comparing pre- and post- spectra
of outgassing
Test for amorphous ice by
searching for exothermic reaction
driving outgassing above
sublimation rate
Determine composition of cool
debris and cometary surface from
spectra
Deep Impact - First Look Inside a Comet
mfa - 53
6. Earth-Based Observing Program
How all astronomers can participate
Earth-Based Geometry
•
•
•
•
•
•
Impact approx 06:00 - 06:30 UTC on 4 July 2005
(a,d) = (13:38, -9.6°); few degrees from Spica
Geocentric Distance = 0.894 AU
Heliocentric Distance = 1.506 AU
Solar Elongation = 104°
Phase angle = 40.9°
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 55
Earth-Based Elevation
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 56
Impact Time
80
70
CTIO
Paranal
Elevation Angle (deg)
60
50
Goldstone
40
30
La Palma
20
Goldstone
Madrid
Paranal
Paranal (Nautical)
Paranal (Day)
CTIO
CTIO (Nautical)
CTIO (Day)
La Palma
La Palma (Nautical)
Teide
Teide (Nautical)
DSN Redundancy
10
Madrid
0
Current baseline
70
2100
2300
0100
Canberra
60
IMPACT!
Baseline at CSR orals
Elevation Angle (deg)
3/4 July 2005 (UT)
Mauna Kea
Mauna Kea (Nautical)
Mauna Kea (Day )
Palomar
Goldstone
Canberra
50
Mauna Kea
40
30
Palomar
20
Goldstone
10
IMPACT!
0
0500
ESO - 14 Feb 2004
0600
Deep Impact - First Look Inside a Comet
0700
0800
4 July 2005 (UT)
mfa - 57
Earth-Based Goals
•
•
Thermal and scattered light curves at high speed
Emission-line spectroscopy at all wavelengths - euv to radio
– Temporal resolution - 1s allowed by photon statistics for strongest
optical lines
– Spatial resolution - limited e.g. to 1 arcsec ~ 700 km, i.e. a point source
•
•
•
X-ray emission
Long-term monitoring
Imaging & morphology at all wavelengths
– Spatial & temporal resolution - significant ejecta to > 1 arcsec takes
tens of minutes although fastest ejecta get there in 5 minutes
– Long-term existence of jets - weeks? months?
– Long-term astrometry for non-gravitational accelerations
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 58
More Info?
•
http://deepimpact.umd.edu/
– Public pages with lots of information
– Mix of technical details and “Middle School” public information
•
http://deepscience.astro.umd.edu/collab/
– Password protected
• User id: dicollab
• Password: tmpl9P
– A special page for collaborating observers (in continuing
development)
– Provides observing circumstances for both professionals and
amateurs
– Provides the ability to enter observing programs into a shared
database for all collaborating observers to see (need your own
registered username)
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 59
Backup Slides
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 60
Phase Functions
Design Case Selected from Many
Adopted Phase Laws for Nucleus and Dust
<<<<<
Nuclei
Ga
-0.252
Phase
[deg]
0
5
10
15
20
25
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
Normalized Phase Fcn
Dust
Nucleus
3
6
<=index 0.030m/deg 0.035m/deg 0.040m/deg
1.000
1.000
1.000
1.000
1.000
0.933
0.755
0.871
0.851
0.832
0.900
0.570
0.759
0.724
0.692
0.847
0.431
0.661
0.617
0.575
0.813
0.325
0.575
0.525
0.479
0.793
0.245
0.501
0.447
0.398
0.793
0.185
0.437
0.380
0.331
0.747
0.106
0.331
0.275
0.229
0.720
0.060
0.251
0.200
0.158
0.710
0.034
0.191
0.145
0.110
0.690
0.020
0.145
0.105
0.076
0.667
0.011
0.110
0.076
0.052
0.747
0.006
0.083
0.055
0.036
0.000
0.004
0.063
0.040
0.025
0.000
0.002
0.048
0.029
0.017
0.000
0.001
0.036
0.021
0.012
0.000
0.001
0.028
0.015
0.008
0.000
0.000
0.021
0.011
0.006
0.000
0.000
0.016
0.008
0.004
0.000
0.000
0.012
0.006
0.003
0.000
0.000
0.009
0.004
0.002
0.000
0.000
0.007
0.003
0.001
index=>
0
1
2
ESO - 14 Feb 2004
Encke
IAU
#NUM!
0.54602
0.38189
0.27957
0.20897
0.15784
0.11976
0.06892
0.03913
0.02190
0.01245
0.00781
0.00597
0.00551
0.00535
0.00479
0.00355
0.00190
0.00058
0.00006
0.00000
0.00000
3
>>>>>
Q
-0.092
Encke
Orig L-B
#NUM!
0.59631
0.44261
0.34287
0.27133
0.21752
0.17597
0.11771
0.08148
0.05951
0.04707
0.04091
0.03858
0.03818
0.03823
0.03765
0.03571
0.03202
0.02646
0.01907
0.01004
0.00000
4
<<<<<
Dust
>>>>>
Gb
0.15
typ ast
IAU
0.061m/deg
#NUM!
1.000
0.67889
0.755
0.55105
0.570
0.46407
0.431
0.39824
0.325
0.34559
0.245
0.30198
0.185
0.23298
0.106
0.18018
0.060
0.13821
0.034
0.10414
0.020
0.07625
0.011
0.05354
0.006
0.03541
0.004
0.02151
0.002
0.01156
0.001
0.00520
0.001
0.00181
0.000
0.00042
0.000
0.00004
0.000
0.00000
0.000
0.00000
0.000
5
6
Deep Impact - First Look Inside a Comet
Ney &
Kiselev &
Merrill
Chernova
C/West P/Ash-Jack C/Meier
1.00
1.0000
1.0000
0.92
0.7447
0.7798
0.85
0.5649
0.6607
0.77
0.5248
0.6138
0.70
0.5346
0.65
0.6026
0.60
0.50
0.45
0.45
0.45
0.45
0.45
0.55
0.80
1.50
2.50
4.00
7.00
10.00
15.00
20.00
0
1
2
Krasno.
P/Halley
1.0000
0.9333
0.9000
0.8467
0.8133
0.7933
0.7933
0.7467
0.7200
0.7100
0.6900
0.6667
0.7467
Schleich.
P/Halley
1.0000
0.9376
0.8872
0.8318
0.7834
0.7447
0.7244
0.6730
0.6486
0.6607
0.6918
3
4
mfa - 61
Target Update – Dust
•
IRAS survey remapped and re-calibrated (January 2000), data from
5 days post-perihelion to several months post-perihelion in 1983;
preliminary models fitted
•
IRAS pointed observations to be recalibrated (one pre-perihelion
observation included)
•
Keck run – August 2000 (7 1/2 months post-perihelion)
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 62
Design Models
•
•
Due to uncertainties, must assume specific models to which
system is designed
Models needed include
–
–
–
–
•
Photometric behavior of dust and nucleus,
Shape and topography of nucleus,
Dust environment,
Cratering process
Must consider worst-case models while designing to a nominal
model
Design models are conservative to encompass cases that are
worse, in whatever sense, than best prediction!
Design models allow flight system design to be mature early!
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 63
Design Model – Photometry
•
Phase function for nucleus derived from recent observations of 2P/Encke
at large phase
• Bi-directional reflectance assumed
• Dust phase function from observations at 1P/Halley
• Dust brightness near opposition scaled from optical observations of
Tempel 1 in 1983
• Nuclear brightness near opposition from HST and UH-88” observations of
Tempel 1 in 1997-1999
_________________
> Average nuclear pixel is brighter than maximum plausible jet brightness at
limb - unlike the case of Giotto at Halley but like Borrelly and Wild 2
> Phase function for nucleus is assumed at dark end of range
> Targeting is straightforward (unlike at Halley)
> Predictions confirmed (within 2x) at Borrelly (DS 1)
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 64
What’s Missing?
•
•
•
•
•
•
Seismometry of impact
Accelerometers on impactor
In situ chemical analysis of gas and dust
Reliable method for measuring mass of nucleus
High spatial resolution at time of impact
Evolution of crater beyond 800 sec
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 65
Crater Scaling
Different Cometary Bulk Densities
Different Target Materials
(Affects Gravitational Acceleration)
Crater Depths
300
50
200
40
200
100
50
150
Depth (m)
Crater Diameter (m)
Crater Diameter (m)
30
20
100
Surface Density = 0.3 g/cc
Cometary Bulk Density = 0.8 g/cc
Surface Density = 0.3 g/cc
Cometary Bulk Density = 0.8 g/cc
Surface Density = 0.3 g/cc
10
100
200
400
600
1000
Impactor Mass (kg)
70
30
100
100
200
400
600
Im pactor Mass (kg)
D ~ m1/6
D ~ rc-1/6
D ~ Rc-1/6
ESO - 14 Feb 2004
1000
200
400
600
1000
Impactor Mass (kg)
Crater depth combines excavation with compression
and displacement. Varies with target material.
Scaling laws use dimensionless parameters discussed,
e.g., in book by Melosh on cratering.
Deep Impact - First Look Inside a Comet
mfa - 66
The Humpty-Dumpty Problem
Species Observed in Comets
Volatile
Atoms
Refractory
Atoms
C
H
(He)
N
O
S
(Ar)
Al
Ca
Co
Cr
Cu
Fe
K
Mg
Mn
Na
Ni
Si
Ti
V
Diatomic
Triatomic
Polyatomic
Ions
C2
CH
CN
CO
CS
NH
NS
OH
S2
SO
(C2H)
C3
CO2
H2O
H2S
HCN
(HCO)
HNC
NH 2
OCS
SO2
C2H2
C2H6
CH3CN
CH3OCHO
CH3OH
CH4
H2CO
H2CS
HC3N
HCOOH
HNCO
NH 3
Mg 2SiO 4
C
+
CH
+
CO
CO2+
H2O+
HCO+
(N2+)
O+
OH+
+
Isotopic
Variants
13
12
C C
13
CN
DCN
H13CN
HC15N
HDO
HDO +
Must use all possible wavelengths and techniques to sort it out
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 67
IRAS and Keck Results
Recalibration of IRAS data
constrains size distribution
of large dust 5 days after
perihelion.
ESO - 14 Feb 2004
Light curve implies dust production is dropping at
perihelion. Allows interpolation or extrapolation of
other data to time of our impact. (Scaling of IR data
to optical data is done empirically.)
Deep Impact - First Look Inside a Comet
mfa - 68
Design Model – Shape
Stooke’s Halley Model
(fit to data)
Gaskell’s Accretion Model
(Theoretical)
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 69
SIM Assembly
The spectral imaging module of
the High Resolution Instrument
consists of an aluminum box
containing mirrors and prisms
carefully placed to guide
photons from the comet,
through prisms, to disperse the
light into its spectral
components and to a focus on
the detector. This unit is sitting
on an optical bench, a strong,
stable and flat platform
designed for high precision
alignments.
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 70
Context – Comets Unknown
•
Mass – no data
– Density and Surface Gravity uncertainty >10x
•
Strength
– Tensile strength < 103dyn/cm2 at km scale
– Nothing else known
•
Stratification
– Know only irradiated mantle on new comets
– Ice to rock ratio unknown
•
Shape
– Data only for 1P/Halley and 19P/Borrelly and now 51P/Wild 2!!
•
Photometric Properties very uncertain
•
Coma dust and rocks very uncertain
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 71
Cratering Flow Pattern
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 72
Crater Section
ESO - 14 Feb 2004
Deep Impact - First Look Inside a Comet
mfa - 73